Scale Model Aircraft Research Articles

Identification of aircraft longitudinal aerodynamic parameters using an online corrective test for wind tunnel virtual flight

The identification of aerodynamic parameters is accomplished through the test data of the dynamic movement of scaled aircraft models flying dynamically in wind tunnel, which can realize the accurate acquisition of the aerodynamic model of the aircraft in the preliminary stage for aircraft design, and it is of great significance for improving the efficiency of aircraft design. However, the translational motion of the test model in the wind tunnel virtual flight is subject to constraints that result in distinct flight dynamics compared to free flight. These constraints have implications for the accuracy of aerodynamic derivatives obtained through the identification of wind tunnel test data. With this issue in mind, the research studies the differences in longitudinal dynamic characteristics between unconstrained free flight and wind tunnel virtual flight, and innovatively proposes an online correction test based wind tunnel virtual flight test technique. The longitudinal trajectory and velocity changes of the model are solved online by the aerodynamic forces measured during the test, and then the coupled relationship between aircraft translation and rotation is used to correct the model’s pitch attitude motion online. For the first time, the problem of solving the data approximation for free flight has been solved, eliminating the difference between the dynamics of wind tunnel virtual flight and free flight, and improving the accuracy of the aerodynamic derivative identification results. The experiment’s findings show that accurate aerodynamic derivatives can be identified based on the online correction test data, and the observed behaviour of the identified motion model has similarities to that of the free flight motion model.

The factorization method and Capon’s method for random source identification in experimental aeroacoustics

Experimental aeroacoustics is concerned with the estimation of acoustic source power distributions, which are for instance caused by fluid structure interactions on scaled aircraft models inside a wind tunnel, from microphone array measurements of associated sound pressure fluctuations. In the frequency domain aeroacoustic sound propagation can be modeled as a random source problem for a convected Helmholtz equation. This article is concerned with the inverse random source problem to recover the support of an uncorrelated aeroacoustic source from correlations of observed pressure signals. We show that a variant of the factorization method from inverse scattering theory can be used for this purpose. We also discuss a surprising relation between the factorization method and a commonly used beamforming algorithm from experimental aeroacoustics, which is known as Capon’s method or as the minimum variance method. Numerical examples illustrate our theoretical findings.

Aircraft Position Prediction during the Crosswind Approach

Testing the impact of the drag coefficient on an F16 aircraft model, depending on the angle of attack a was performed. First, a navigation model was introduced describing the preliminary and computational assumptions of the model. The final part of the present paper contains the relationships between the wind angle and the wind correction angle at the angle of attack a = 00, a = 110, a = 130 for a full-scale F-16 aircraft. The tables present results of all the calculations for individual angles of attack, taking into account variable wind angles relative to the longitudinal axis of the runway. The values show the corrections calculated for an 1/19 scale aircraft model and for a full-scale F16 aircraft. The "right" and "left" designations represent the direction from which the wind blows in relation to the aircraft.

Flight safety oriented ice shape modulation using distributed plasma actuator units

Ice accretion on the wings seriously threatens the flight safety of an aircraft. From the perspectives of ensuring flight safety and saving power consumption, the ice shape modulation method using distributed plasma is proposed. Distributed plasma actuator units are designed to modulate the spanwise continuous ice at the leading edge into periodically segmented ice pieces, forming a wavy leading edge. Both airfoil and scaled aircraft model, with continuous and modulated ice, are experimentally investigated and simulated. Compared with the continuous ice, ice shape modulation can significantly improve the aerodynamic performance, flight control characteristics and flight safety. This method can save about half electric power, which is very beneficial for application.

3D Generalized Inverse Beamforming in wind tunnel aeroacoustic testing: application to a Counter Rotating Open Rotor aircraft model

Inverse methods are gaining relevance in the aeroacoustic community for their capability to accurately localize and quantify noise sources. Indeed, since modern aircraft are more targeted to the reduction of fuel consumption, and very often some design choices, like Open Rotor (OR) propulsion systems, cause excessive acoustic emissions, accurate knowledge of noise source locations is of fundamental importance. This paper describes the use of an inverse method, namely Generalized Inverse Beamforming (GIBF), to characterize a Counter Rotating Open Rotor (CROR) installed on a 1/7th scale aircraft model. The model was tested in a large Low-Speed Wind Tunnel (WT) at The Pininfarina Aerodynamic and Aeroacoustic Research Center in Turin, Italy, within the framework of the FP7 EU Clean-Sky WENEMOR (Wind tunnel tests for the Evaluation of the installation effects of Noise EMissions of an Open Rotor advanced regional aircraft) project. With respect to previous works already published, the pros and cons of 3D GIBF formulation will be discussed on data collected from an industrial test case. A comparison of L2 and L1 norm formulations, as well as multiplicative approach and single array processing in 3D GIBF, will be performed, discussing their differences in terms of source localization accuracy. Since a quantitative analysis on real data cannot be provided because of confidentiality issues, the capability of the present approach to correctly quantify the source strength will be evaluated by considering a synthetic monopole source emitting white noise at different signal-to-noise-ratios (SNRs). Finally, it will be shown that 3D GIBF can provide engineers with more reliable data regarding the acoustic behavior of CROR-based aircrafts, this proving the advantages in exploiting this inverse method in WT aeroacoustic applications.

Safety assessment of Generation Ⅲ nuclear power plant buildings subjected to commercial aircraft crash Part I: FE model establishment and validations

Abstract Investigations of the commercial aircraft impact effect on nuclear island infrastructures have been drawing extensive attention, and this paper aims to perform the safety assessment of Generation Ⅲ nuclear power plant (NPP) buildings subjected to typical commercial aircrafts crash. At present Part I, finite element (FE) models establishment and validations for both the aircrafts and NPP buildings are performed. (i) Airbus A320 and A380 aircrafts are selected as the representative medium and large commercial aircrafts, and the corresponding fine FE models including the skin, beam, fuel and etc. are established. By comparing the numerically derived impact force time-histories with the existing published literatures, the rationality of aircrafts models is verified. (ii) Fine FE model of the Chinese Zhejiang Sanao NPP buildings is established, including the detailed structures and reinforcing arrangement of both the containment and auxiliary buildings. (iii) By numerically reproducing the existing 1/7.5 scaled aircraft model impact tests on steel plate reinforced concrete (SC) panels and assessing the impact process and velocity time-history of aircraft model, as well as the damage and the maximum deflection of SC panels, the applicability of the existing three concrete constitutive models (i.e., K&C, Winfrith and CSC) are evaluated and the superiority of Winfrith model for SC panels under deformable missile impact is verified. The present work can provide beneficial reference for the integral aircraft crash analyses and structural damage assessment in the following two parts of this paper.

비 챔버 환경에서의 항공기 축소 모형에 대한 모노스태틱 레이다 단면적 측정 방법

This paper presents a method for measuring the radar cross section(RCS) of a scaled aircraft model with a low RCS value in environments other than electromagnetic anechoic chambers. We improve measurement accuracy by introducing coherent integration, coherent subtraction, and time-gating techniques to both eliminate the echoes of non-target objects and improve the signal-to-noise ratio. In this manner, we obtain measurement results that are consistent with the simulation results for complex structures even in environments where many error factors exist.

Novel Approach to Dynamic Soaring Modeling and Simulation

This paper revisits dynamic soaring on the basis of a nonlinear point-mass flight dynamics model previously used for scale-model aircraft to design path-following autopilots endowed with theoretically and experimentally demonstrated stability and convergence properties. The energy-harvesting process associated with specific maneuvers of a glider subjected to horizontal wind, and on which dynamic soaring relies, is explained in the light of this model. Expressions for the estimates of various variables involved in dynamic soaring along inclined circular paths crossing a thin wind shear layer, as experienced by model glider pilots over the world, are derived via approximate integration of the model equations. Given a glider’s path and a wind profile, this model also presents the asset of yielding an explicit ordinary differential equation that entirely characterizes the time evolution of the modeled glider’s state along the path, thus allowing for an easy simulation of dynamic soaring over a large variety of operating conditions. This simulation facility is viewed as a tool that usefully complements other studies of dynamic soaring that focus on trajectory optimization via dynamic programming. Its usefulness is here illustrated by first validating the aforementioned estimates in the case of circular trajectories crossing a thin wind shear layer, and then by showing how it applies to other examples of trajectories and ocean wind profile models commonly considered in studies about the dynamic soaring abilities of albatrosses.

Validation of Control Laws at High Angles of Attack Using Three-Degree-of-Freedom Dynamic Rig in Wind Tunnel

Abstract The paper presents a technique for cost-effective and safe study of conventional and critical flight regimes and control validation using an autonomous dynamically scaled aircraft model mounted in a three-degree-of-freedom gimbal in a wind tunnel. The similarity of the dynamics of the model in gimbal and in free flight at high angles of attack is shown. To suppress large amplitude self-sustained pitch oscillations and prevent stalling, several control laws are developed using recent control design techniques based on structured H∞-optimization. The control laws are tested and compared in a dynamic rig with three degrees of freedom in a wind tunnel.

The concept and methodical assumptions for the development of dynamically scaled aircraft model (passenger aircraft)

The article describes the concept of scaled model and its application in the process of real aircraft prototyping. Computer simulations of aerodynamic flows are commonly used in the design of aircraft. Numerous data on the characteristics of an airplane can be obtained using tunnel tests of geometry scaled models. To get complete information in extreme or unstable conditions, dynamically scaled models are tested. The scaled model is reduced model of the real airplane which has specific qualities similar to real aircraft qualities and these relations are strictly defined with characteristic similarity numbers (factors). The paper presents methodology for determining scale factors in relation to geometric, aerodynamic and structural properties (mass, stiffness) of the aircraft. The methodology was presented on the example of passenger aircraft (Tu-154M) model developed in Faculty of Mechatronics and Aerospace of the Military University of Technology (FMA MUT Warsaw, PL).

Airframe noise measurements in a large hard-walled closed-section wind tunnel

The airframe noise of a 1:2 scaled aircraft model is investigated through a series of experiments in the hard walled closed test section of a large non-anechoic wind tunnel. A surface mounted phased microphone array is used to acquire the wall pressure fluctuations generated by the interaction of the wind tunnel flow and the propagating noise. Data from two measurement campaigns are analysed. The wind tunnel acoustic behaviour and the array performance are first assessed evaluating the results obtained from a reference sound source installed in the centre of the test section. The combination of different airflow speeds, array positions and sound sources are tested. The airframe noise is evaluated acquiring pressure fluctuations in different configurations. The main parameters varied during the tests are the flight configuration, the speed of the airflow, the incidence angle of the model and the position of the microphone array. Data are processed and then analysed in the frequency domain and using a conventional beamforming algorithm to retrieve the sound source maps over the regions of interest. Source maps are deconvolved with a CLEAN-SC routine and single source contributions determined through integration of auto-powers. The resulting spectra are finally scaled determining the exponents of the pertinent scaling laws.

Comparison of computational and experimental microphone array results for an 18% scale aircraft model

An 18%-scale, semispan model is used as a platform for examining the efficacy of microphone array processing using synthetic data from numerical simulations. Two hybrid RANS/LES codes coupled with Ffowcs Williams-Hawkings solvers are used to calculate 97 microphone signals at the locations of an array employed in the NASA LaRC 14×22 tunnel. Conventional, DAMAS, and CLEAN-SC array processing is applied in an identical fashion to the experimental and computational results for three different configurations involving deploying and retracting the main landing gear and a part-span flap. Despite the short time records of the numerical signals, the beamform maps are able to isolate the noise sources, and the appearance of the DAMAS synthetic array maps is generally better than those from the experimental data. The experimental CLEAN-SC maps are similar in quality to those from the simulations indicating that CLEAN-SC may have less sensitivity to background noise. The spectrum obtained from DAMAS processing of synthetic array data is nearly identical to the spectrum of the center microphone of the array, indicating that for this problem array processing of synthetic data does not improve spectral comparisons with experiment. However, the beamform maps do provide an additional means of comparison that can reveal differences that cannot be ascertained from spectra alone.

Dynamic Rig for Validation of Control Algorithms at High Angles of Attack

The dynamics of a modern aircraft at high angles of attack is complicated, with hazardous phenomena such as wing rock, stall, and spin. The paper presents a technique for cost-effective and safe studying of conventional and critical flight regimes and control validation using an autonomous scaled aircraft model mounted in a three-degree-of-freedom gimbal in a wind tunnel. The similarity of the dynamics at high angles of attack of the wind-tunnel model and the free-flying model is demonstrated. To suppress the wing rock and to prevent the stall, two control laws are designed using linear matrix inequalities and model reference adaptive control techniques. The controllers are tested in a semifree flight of the autonomous scaled model in the wind tunnel. Wing rock suppression and stall and spin prevention are demonstrated.

Multi-dimensional scattering properties diagnosis system of scale aircraft model in an anechoic chamber

Aiming at the concept of “diagnosis“, a simple and effective broadband radar cross section (RCS) measurement system is constructed, and some multi-dimensional scattering properties diagnosis techniques are presented based on the system. Firstly, a stepped-frequency signal is employed to achieve high range resolution, combining with a variety of signal processing techniques. Secondly, cross-range resolution is gained with a rotating table, and the high-resolution two-dimensional (2-D) imaging of the scale model is obtained by the microwave imaging theory. Finally, two receiving antennas with a small distance in altitude are used, and the three-dimensional (3-D) height distribution of scattering points on the scale model is extracted from the phase of images. Some typical bodies and a scale aircraft model are diagnosed in an anechoic chamber. The experimental results show that, after scaling with a metal sphere, the accurate one-dimensional (1-D) RCS pattern of the model is obtained, and it has a large dynamic range. When the bandwidth of the transmitting signal is 4 GHz, the resolution of the 2-D image can reach to 0.037 5 m. The 3-D height distribution of scattering points is given by interferometric measurement. This paper provides a feasible way to obtain high-precision scattering properties parameters of the scale aircraft model in a conventional rectangular anechoic chamber.

FEM Analysis of Impact Tests for Steel Plate Concrete Panels against Scaled-Aircraft Impact

Due to the rear-face steel plate of the steel plate concrete wall (SC) is very effective in preventing the perforation and scabbing of concrete, in order to resist the impact of commercial aircraft crash, steel plate concrete structures are usually used in the design of external walls of nuclear power plants. In this paper, the simulation analysis of the impact test of 1/7.5 scaled aircraft model impacting the steel plated concrete panels is carried out by using finite element code ANSYS/LS-DYNA. The Winfrith material model (*MAT_84) in ANSYS/LS-DYNA is used to simulate the concrete. The damage profile of panels and residual velocity of aircraft engine comparisons between the simulations and tests are presented in this paper. The results indicate that the damage modes from the impact simulations are very good agreement with the experimental result. It is verified that not only the selection of the material parameters needed for the steel plated concrete wall and aircraft model but also the entire analysis method was appropriate and effective. This paper provided the effective methodology for simulation of the response of the steel plated concrete structure of nuclear power plant due to commercial aircraft crash impact.

Scaled Bistatic Radar Cross Section Measurements of Aircraft With a Fiber-Coupled THz Time-Domain Spectrometer

The knowledge of the radar cross section (RCS) of aircraft and other objects is of great interest both for civil and military applications. Scaled setups are often used in order to facilitate RCS measurements in a well-defined laboratory environment. As radar frequencies steadily increase, for high scaling factors these measurements have to be carried out in the THz regime. In this paper, we propose an experimental setup consisting of a fiber-coupled THz time-domain spectrometer integrated with a two circle goniometer, which enables bistatic scaled RCS measurements. To assess the accuracy of the setup, measurements on reference objects as well as on scale model aircraft are performed. The measured data of the reference objects is compared to the theoretical predictions. As for the aircraft, the comparison between a Panavia 200 Tornado and a Lockheed F117 Nighthawk is made and the influence of individual components like bombs on the overall RCS is evaluated.

Terahertz radar cross section measurements

We perform angle- and frequency-resolved radar cross section (RCS) measurements on objects at terahertz frequencies. Our RCS measurements are performed on a scale model aircraft of size 5-10 cm in polar and azimuthal configurations, and correspond closely to RCS measurements with conventional radar on full-size objects. The measurements are performed in a terahertz time-domain system with freely propagating terahertz pulses generated by tilted pulse front excitation of lithium niobate crystals and measured with sub-picosecond time resolution. The application of a time domain system provides ranging information and also allows for identification of scattering points such as weaponry attached to the aircraft. The shapes of the models and positions of reflecting parts are retrieved by the filtered back projection algorithm.

One-Dimensional Frequency-Domain Features for Aircraft Recognition from Radar Range Profiles

To extract effective one-dimensional frequency-domain features from high-resolution radar range profiles, the differential power spectrum (DPS) and the product spectrum, which were originally proposed for the speech signal processing, are introduced to the radar target recognition community. Through differentiating the power spectrum with respect to frequency, we obtained the DPS, which is translation invariant. The DPS can preserve the spectral information contained in the range profiles. The product spectrum is defined as the product of the power spectrum and the group delay function. Thus, it can combine the information contained in the magnitude spectrum and phase spectrum of the range profiles and then carry more details about the shape of the aircrafts. In the classification phase, an optimal choice can be determined by implementing six different training algorithms of multilayered feed-forward neural network. The range profiles were measured by using the two-dimensional backscatters distribution data of four different scaled aircraft models. Simulations were demonstrated to evaluate the classification performance with the DPS and the product spectrum-based features. The simulation results have shown that both DPS and product spectrum-based features are effective for the automatic target recognition (ATR) of aircrafts.

Characterizing Stability and Control of Subscale Aircraft from Wind-Tunnel Dynamic Motion

This paper outlines a process of determining the stability and control characteristics of small-scale aircraft from wind-tunnel experiments which aim to emulate flight tests. Scaled aircraft models with representative control surfaces are flown in semifree flight on a test rig allowing motion in 4 degrees of freedom. The motion is measured and system identification and parameter estimation techniques are used to obtain a mathematical description of the dynamics of the model. Previous work has relied on the use of potentiometers to measure the model's attitude about its pivot point with other motion variables being generated analytically using these measurements and well-known kinematic relationships. However, it is now possible to mount sensors within the model as advances in technology have produced microelectromechanical system packages of small size, lightweight, low cost, and low power consumption. The current work is investigating the effectiveness of using microelectromechanical system inertial sensors to measure motion of the model. An example of the system identification process carried out on a one-twelfth scale BAe Hawk model is also presented. Parameter estimation is performed in the frequency domain using the equation error and output error methods.

Comparison and Application of Near-Field ISAR Imaging Techniques for Far-Field Radar Cross Section Determination

Inverse synthetic aperture radar (ISAR) imaging is a powerful tool for the characterization of scattering properties of radar targets. In particular, near-field techniques allow for short distance imaging with results comparable to those of standard far-field ISAR techniques. The resulting near-field images can be used to extract the far-field radar cross section (RCS) of the target overcoming the need for long-range measurement setups. This paper compares different near-field imaging techniques and reveals an in-depth insight into the imaging process, especially with regard to the subsequent RCS extraction. The performance of the different techniques together with processing improvements are demonstrated by means of numerical target models as well as by measured data of test objects and a scaled aircraft model.